The field of the present invention is shutters for movie cameras or the like.
A motion picture camera exposes film by allowing light to pass through a lens opening and then through a shutter aperture. The shutter rotates at a speed synchronous with that of the passing film frames. One form of prior art shutter is shown in FIGS. 1a and 1b illustrating what will be called the stationary or main shutter wheel 10 and the adjustable shutter wheel 20. Both the main shutter wheel 10 and the adjustable shutter wheel 20 are generally of a bow tie-like shape and rotate about a shaft on an axis 5 at a speed which is synchronous with that of the film. Inside the camera, the film is positioned to be exposed to light through the apertures between the two opposing shutter elements or extensions 10a and 10b. Referring to FIG. 1a, as the stationary shutter wheel 10 rotates, light passes through the camera lens onto the film frame which is aligned behind the shutter aperture for the amount of time the aperture is so aligned allowing the film to be exposed. The film is advanced from one frame to the next frame while the light path is interrupted by the shutter elements 10a and 10b. Thus two frames of films are exposed and advanced for each revolution of the shutter 10.
In order to control exposure, a second shutter wheel, the adjustable shutter wheel 20, is included. The adjustable shutter wheel 20 rotates with the shutter wheel 10 and therefore also rotates at a synchronous speed with the film. By an adjustment mechanism, the adjustable shutter wheel 20 may be pivotally adjusted relative to the stationary shutter wheel 10. The adjustable shutter wheel has two shutter extension members 20a & 20b which may cover some portion of the two apertures between stationary shutter wheel elements 10a & 10b. By pivoting the adjustable shutter wheel 20 relative to shutter wheel 10, a portion of the arc of each aperture may be covered by the rotating shutter extensions 20a & 20b.
With the prior art shutter arrangement of FIGS. 1a and 1b, it has been conventional to provide shutter elements 10a, 10b, 20a and 20b with an arcuate extent of about 80.degree. whereby with those shutter elements exactly superimposed, as shown in FIG. 1a, the two apertures are 100.degree. each. An aperture of this size provides a highly acceptable amount of light to the film to allow better lens stop settings than if the aperture was smaller but it also makes it impossible to completely close the 100.degree. apertures with the 80.degree. shutter elements 20a and 20b. Moreover, the closing of the aperture progresses in only one direction at one time with respect to the stationary shutter 10, i.e. such as clockwise, whereby the location of the aperture becomes asymmetrical with respect to shutter 10 and, for example, with the timing of the film movement. This asymmetry can be undesirable when attempting to create certain cinematographic effects.
There are other conventional rotating adjustable shutters for movie cameras that differ from the shutter of FIGS. 1a and 1b, such as those having two aperture openings of about 88.degree. each but the light admitted thereby is too restricted, particularly in low light level conditions. Another prior art adjustable rotating shutter uses a single shutter element which creates a single aperture but it has the similar deficiencies and the additional problem of balancing.